What's the theory behind that Matt?

 

Mechanical secondarys open the second u give it gas, vacume take time for load, before they open, to rev up a car and dump it with a vacume secondarys would be robbing those other 2 barrels, because the engine wouldnt be under load to open them -Jon

 

honestly id look into a 750 for ur cleve with the mods uve done

 

The DP doesn't open the secondaries right away, they wait until you're about 1/2 throttle. And they definitely ROAR.

DP's have progressive linkage that allows only the primaries to work under 1/2 throttle, which definitely help mileage and response. I've seen increases in mileage by switching to a DP from a vacuum secondary.


BTW, if a vacuum secondary gives a huge kick, it isn't adjusted quite right. Same for a DP. You really shouldn't notice a huge transition, just a bump in the amount of thrust you're feeling on your backside. But, adjusting a vacuum secondary is part of the reason I won't run one. Too much tuning effort that could be use for something more fun...like driving.

 

hmm, i can either buy this 650 holley DP or a 750 holley vacuum secondaries, the 750 is $50 more expensive but it sat for 2 years. the 650 is rebuilt and the other is NIB

what one would YOU go for?[:-]

 

whats your car runnign now?
i'd buy the dp...you can always sell it again if you dont like it or its too small. either way you'll find out

 

650 edelbrock that wa "leaned for efficiency" but the PO tuned it to run rich

 

the ebrocks arent too bad as far as holing a tune but i like the idea of the adjusta-jet for the holly carbs

 

whats a holley double pumper spread bore? what is spread bore?

 

To start dp's are progressive in the opening of the throttle plates unless you have a diominator or another 'center squiter'. The throttle response is very good and you will come off the corners harder in the mid-range. If you have the carb jetted properly the fuel milage is no worse than the same size vacumn secondary driven the same way. When you say 'no choke' do you mean no choke plate or no choke tower? BIG difference. If your 351-c has any upgrades like cams or headers I'd recommend the 750dp Holley.
Also, does it have a 4-corner idle? If it does you circulate fuel from both bowls all thte time and the fuel in the back does not stagnate. This design will also allow you to run some VERY radical cams and still idle without drilling holes in your throttle plates in the front.
Good luck.

Oh, 1 more thing..you will need a very good electric pump mounted ot back to keep-up with fuel demand.